For being one of your first programs I think your on the right track!! At a glance, your game could be slowing down because you are loading things in your functions and not in your initialization section before the main loop.
for example in this function you loaded enemyship in your function, which I have learned is a bad thing
;=======================
Function drawenemy()
enemyship = LoadImage ("C:\blitzpics\alien.jpg")
;=========================
as for the flickering, I myself have always set my buffer right after the initial graphicsmode call. I have encountered screen flickering like you described and it was when I had used the flip command too much or in an inconvenient place.
-Soo hope any of this helps some
for example in this function you loaded enemyship in your function, which I have learned is a bad thing
;=======================
Function drawenemy()
enemyship = LoadImage ("C:\blitzpics\alien.jpg")
;=========================
as for the flickering, I myself have always set my buffer right after the initial graphicsmode call. I have encountered screen flickering like you described and it was when I had used the flip command too much or in an inconvenient place.
-Soo hope any of this helps some